The Intel 4004 is a 4-bit central processing unit (CPU) released by Intel Corporation in 1971. Sold for US$60, it was the first commercially produced microprocessor, and the first in a long line of Intel CPUs.
Intel C4004 processor with grey traces
Intel 4004 CPU and associated chips on the circuit board from a Busicom calculator
The Unicom 141P is an OEM version of the Busicom 141-PF.
Intel 4004 advertisement in Electronic News magazine from 1971
4-bit computing is the use of computer architectures in which integers and other data units are 4 bits wide. 4-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers or data buses of that size. A group of four bits is also called a nibble and has 24 = 16 possible values.
20-pin PSOP – NEC D63GS: a 4-bit microcontroller for infrared remote control transmission
16-pin DIP – Intel C4004
Infrared remote control PCB – an infrared remote control transmitter controlled by a NEC D63GS 4-bit microcontroller
National Semiconductor MM5700CA/D bit-serial 4-bit microcontroller